1. Field of the Invention
This invention relates to a duplex (two sides) copying apparatus which can selectively perform either one side copying or two sides copying, as compared to a conventional type which employs only one side copying onto a transfer material.
2. Description of the Prior Art
Prior art copying apparatus are generally those which provide an image only on one side of a transfer material. According to such a previous method, however, in case of storing a great amount of copied materials, the copied material will be doubled, as compared with copied material made by the duplex copying, which is disadvantageous in respect of storing space, weight, cost, and the like.
There have been considered several types of duplex copying apparatuses in the form of transfer systems. First, there is a type in which separate images are formed on two photosensitive drums for the subsequent transfer thereof to the respective surfaces of a transfer material. However, this type is simple in its principle but requires two sets of copying processes, and therefore the apparatus will be expensive and larger in size. Second, there is a type in which an image of one surface is first formed on the photosensitive drum and then transferred to a medium drum to hold it thereon for the time being, and an image of the other surface is successively formed on the same photosensitive drum. Thereafter the images are transferred to the transfer material from the medium drum and the photosensitive drum. In this type, there is required only one set of copying process elements, but two transfers should be made through the aid of the medium drum, which deteriorates the transfer efficiency. Third, there is a type in which one side of a transfer material is first treated with a conventional one side copying, the transfer material, one side of which has been copied, is again introduced into an original feeding device or a second feeding device, and the material is turned upside down and fed into the copying apparatus for effecting a conventional one side copying on the back. In this third type, there is required only one set of copying process elements, as in the one side copying device, which provides an inexpensive and compact apparatus and serves as a most practical duplex copying apparatus,
However, the third type just mentioned also has problems concerning (1) a method for reversing a transfer material, one side of which has been copied, when it is fed into the copying apparatus again; (2) a method for properly arranging a transfer material, one side of which has been copied, when it is put on the feeding device; (3) a method for securely separating one by one and delivering the material from the feeding device when it is fed into the copying apparatus for the second time; (4) a method for copying with a large amount of duplex copying; and (5) a duplex copying method which can select either one side copying or duplex copying in case of necessity.